In an operating room, the anesthesiologist needs to assess the patient's condition and adjust the therapy using a wide variety of distinct medical devices. These devices often don't talk to each other, and hence only provide one piece of the picture. Clinicians have to mentally keep track of the patient's level of sedation, analgesia and relaxation based on the amount of drugs they've administered, and their familiarity with the drug's pharmacokinetic/pharmacodynamic (PK/PD) models.
The practice of intra-operative anesthesia typically involves administering sedative, analgesic and neuromuscular relaxants to a patient. These drugs manage the patient's level of consciousness, pain management and neuromuscular blockade. Typically, each drug has a PK/PD model that specifies what the body does to the drug (PK) and how the drug interacts with the body (PD). These models are usually derived in isolation. In a clinical setting multiple drugs are typically used together.
Three-dimensional response surfaces have been developed to represent the interaction between two drugs. These surfaces represent the probability of non-response to a specific effect at different concentrations of the two drugs. This can also be considered an interaction (or synergistic) PD model. The challenge is to display these varying probabilities on a 2d graph that can easily be interpreted by a clinician during anesthesia.
The issue is confounded even more when there is more than one effect to display on the same graph. For example, when considering analgesia, one can consider varying levels of pain such as high pain, such as that experienced in intubation, and low pain, such as that experienced in post-operative analgesia. The challenge is to display these related but distinct surfaces on the same two-dimensional graph. The display should consist of the effect site concentration of the analgesic drugs which is at least one input to the 3d surface. The probability of each displayed effect, and reference points to those effects (such as 50% to 95% probability.)
Furthermore, typical anesthesia practice involves various combinations of drugs, which may not be fully supported by the response surface model. For example, a typical case may start with a propofol-remifentanil induction, and then proceed with isoflurane and remifentanil. Interactions between Propofol, isoflurane and remifentanil are not fully known at this time. Furthermore, use of antagonists—drugs that reverse the effects of other drugs—invalidate the primary drug's pharmacokinetic properties and need to be accounted for in the display.